The sense of hearing in human beings involves the use of hair cells in the cochlea that convert or transduce acoustic signals into auditory nerve impulses. Hearing loss, which may be due to many different causes, is generally of two types: conductive and sensorineural. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded. These sound pathways may be impeded, for example, by damage to the auditory ossicles. Conductive hearing loss may often be overcome through the use of conventional hearing aids that amplify sound so that acoustic signals can reach the hair cells within the cochlea. Some types of conductive hearing loss may also be treated by surgical procedures.
Sensorineural hearing loss, on the other hand, is caused by the absence or destruction of the hair cells in the cochlea which are needed to transduce acoustic signals into auditory nerve impulses. People who suffer from sensorineural hearing loss may be unable to derive significant benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is. This is because the mechanism for transducing sound energy into auditory nerve impulses has been damaged. Thus, in the absence of properly functioning hair cells, auditory nerve impulses cannot be generated directly from sounds.
To overcome sensorineural hearing loss, numerous cochlear implant systems—or cochlear prostheses—have been developed. Cochlear implant systems bypass the hair cells in the cochlea by presenting electrical stimulation directly to the auditory nerve fibers. Direct stimulation of the auditory nerve fibers leads to the perception of sound in the brain and at least partial restoration of hearing function.
To facilitate direct stimulation of the auditory nerve fibers, a lead having an array of electrodes disposed thereon may be implanted in the cochlea. The electrodes form a number of stimulation channels through which electrical stimulation pulses may be applied directly to auditory nerves within the cochlea. An audio signal may then be presented to a patient by translating the audio signal into a number of electrical stimulation pulses and applying the stimulation pulses directly to the auditory nerve within the cochlea via one or more of the electrodes.
Conventional cochlear implant systems include external components that are worn on the head and/or ear of a patient. The external components typically include a microphone for detecting sounds in the patient's environment, audio processing circuitry for modifying, digitizing, and/or amplifying the detected sounds, and a transmitter for sending radio frequency signals representative of the detected sounds to an implanted cochlear stimulator. Such external components are often relatively large, cumbersome, and noticeable by others.
Hence, many patients would prefer a fully implantable cochlear implant system that does not include unsightly external components. However, fully implantable cochlear systems have certain limitations. For example, a microphone implanted beneath a patient's skin may detect bodily noises (e.g., the patient's heartbeat) that may interfere with the quality of the patient's listening experience. Additionally, components within a fully implantable cochlear implant system may become degraded or damaged during use. Oftentimes, surgery may be required to properly repair and/or upgrade such components. Accordingly, a patient may desire the capability to optionally use external components in conjunction with a fully implantable cochlear implant system to compensate for and/or to enhance the performance of the implanted components.